Thank you so much.
May I ask how to use Fourier analysis please? Could you please give me some details? I'm quite bad with Fourier series, it has been one weakness for me for a long time.
Thanks a lot.

Thank you so much.
May I ask how to use Fourier analysis please? Could you please give me some details? I'm quite bad with Fourier series, it has been one weakness for me for a long time.
Thanks a lot.

Use the Fourier series for the half-range even periodic extension of the function where and apply Parseval's Theorem. (And no, I'm not going to do the calculation, that's your job if you want it).